1. Field of the Invention
The present invention relates generally to the production of synthetic diamonds and diamond materials and more particularly, to the production of doped synthetic diamonds and diamond materials.
2. Description of the Prior Art
Diamond based semiconductors have several desirable properties that include a wide bandgap, high carrier mobility, a large thermal conductivity, and chemical inertness. Diamond electronic devices can potentially operate at much higher temperatures than Si devices, due to the larger bandgap, which reduces the number of thermally excited carriers. The high thermal conductivity of diamond may also permit one to fabricate high power/density devices and circuits of diamond without jeopardizing the performance due to thermally induced temperature increases. Semiconductor photoemitters and photodetectors formed out of diamond have the possibility of operating in regions of the UV not easily accessible to other semiconductor materials. Doped diamond optical devices, such as lasers, also offers exciting possibilities. Creating diamond-based electronic and photonic devices requires an understanding of the electrical properties of diamond along with the capability to grow high quality diamond.
Doped single crystal diamond is available from low pressure chemical vapor deposition (CVD) processes using hydrocarbon gases (see Fujimori, et al., "Characterization of conducting diamond films" Vacuum, Vol. 36, Nos. 1-3, pages 99 to 102 (1986), incorporated herein by reference) and from natural sources. Type IIB natural diamonds contain boron, and type IB diamonds contain nitrogen, however natural diamond is not useful for electronic devices because of the inability to control the dopant level. Doping of crystals grown with General Electric's high pressure high temperature (HPHT) process has been reported but the doping profile cannot be tailored and thus this process is not practical. Hence the only practical way of fabricating electronic devices made of diamond is with CVD processes. Current rates for the CVD synthesis of epitaxial diamond are slow (.about.1 micron/hour), and do not always produce high quality diamond.
Recently, several new techniques for the low pressure production of high quality synthetic diamonds by flame and/or plasma torch deposition have been described. These techniques are described in, for example in U.S. patent application Ser. No. 07/587,328, entitled FLAME OR PLASMA SYNTHESIS OF DIAMOND UNDER TURBULENT AND TRANSITION CONDITIONS, filed Sep. 24, 1990 to Snail et al.; U.S. patent application Ser. No. 07/548,719, entitled EPITAXIAL SYNTHESIS OF DIAMOND CRYSTALS AT HIGH GROWTH RATES, filed Jul. 6, 1990 to Snail et al.; Snail et al., Appl. Phys. Lett., 58, 1 (1991); snail and Hanssen, J. Crystal Gr., 112(4) 651 (1991) , the entirety of all of which are incorporated herein by reference. In particular, diamonds produced under turbulent and transition conditions (as defined in the above-mentioned Snail et al. '328 patent application, i.e., transition of Reynolds number .about.1200 to 2200 and have been of exceptionally high quality, and monocrystalline, bulk diamonds have been grown epitaxially at high substrate temperatures (about 1200.degree. to about 1500.degree. C.). The Raman spectra of the turbulently grown films shows a noticeable lack of non-diamond carbon peaks and the high luminescence background that had previously been observed with diamond grown in laminar oxy-acetylene flames. The low temperature photoluminescence spectrum of turbulently grown diamond films exhibits no detectable vacancy related complexes, and is dominated by a strong first order Raman phonon line as well as a low, broad almost featureless emission band. To the human eye, undoped films appear white with no tint or discoloration. The lack of localized electrical defects, as shown by optical measurements indicates that this particular growth technique can produce diamond suitable for electronic applications, especially if they can be doped in a controlled manner. Since the Debye temperature for diamond is 1600.degree. C., processes for growing diamond epitaxially at high temperatures (1200.degree.-1600.degree. C.) with laminar or turbulent flames and plasma torches permits higher doping efficiencies and dopant levels compared to lower temperature deposition processes.